This invention relates to the encapsulation of core material within a semipermeable membrane. More particularly, the invention relates to a process for encapsulating pH, temperature, or ionic strength-sensitive core material, including viable cells, within a microcapsule. The encapsulation process disclosed herein allows formation of a semipermeable membrane without damaging the core material. The invention also relates to a capsule having an aminated polymeric inner layer ionically bound to an anionic polymeric outer layer.
Although a number of processes for microencapsulation of core material have been developed, most of these processes can not be used for pH, temperature or ionic strength-sensitive material such as viable cells because of the harsh conditions necessary for encapsulation. U.S. Pat. No. 4,352,883 discloses what is believed to be the first process for successfully encapsulating viable tissue or cells within a semipermeable membrane. In the patented process, a temporary capsule of a gellable material, preferably an anionic gum such as sodium alginate, is formed about the tissue or cells and a permanent, semipermeable membrane is formed by cross-linking surface layers of the temporary capsule. Specifically, a mixture of the gum and the core material is subjected to a gelling solution, preferably a calcium ion solution, to produce a temporary capsule. The resulting temporary capsule is reacted with a solution of a polycationic material to form a permanent membrane. The interior of the capsule may be reliquified by reestablishing conditions under which the anionic gum is liquid, e.g., changing the ionic environment by placing the capsules in phosphate buffered saline. Reliquification of the interior of the capsule facilitates nutrient transport across the membrane, promoting cell growth. The process need not damage the core material or hamper the viability of cells because the temperature, ionic strength, and pH ranges used in the encapsulation process need not be harsh.
Accordingly, an object of the invention is to provide a process for encapsulating viable cells or other fragile material in semipermeable membranes. Another object is to provide a process for encapsulating core materials which are difficult to capsulate using known procedures because of pH, ionic strength, charge, or temperature sensitivity. A further object of the invention is to provide an improved capsule comprising a semipermeable membrane. These and other objects and features of the invention will be apparent from the following description.